1. Field of the Invention
The present invention relates to an upper fork provided in a front fork assembly constituting an essential part of a suspension system for a front road wheel of a motorcycle, the system including a link motion arrangement therein.
2. Related Art
In a suspension system for a front road wheel of a motorcycle, it is known to employ a telescopic type front fork for suspending the front road wheel including fork pipes and slidable bottom cases which constitute hydraulic shock absorbers. Another type of a suspension system which employs a link motion therein is also known, for example, from U.S. Pat. No. 4,212,481, issued to Valentino Ribi on July 15, 1980.
This particular link motion type suspension system includes an upper fork supported on a body frame, and a swingable lower fork supporting a front road wheel thereon. In such suspension system, damping actions are obtained through a shock absorber having one end joined to either one of the two forks and the other end operatively connected to the other one of the two forks through links.
The upper fork of such a front fork assembly acts as the support for rocking motion of the lower fork, the support for pivotal motion of arms, the support on the motorcycle body, and the support of the shock absorber, and receives reaction forces and shocks through these various parts. Therefore, a sufficient strength and rigidity is required. If the strength and rigidity were to be improved, however, the upper fork would have a harder profile and an increased weight. Moreover, forming of the upper fork by cutting or by casting would make production thereof troublesome and increase production costs and the weight thereof. The present invention is directed toward overcoming such problems.